Electrolyte membrane for fuel cell and fuel cell using the same

ABSTRACT

A fuel cell including an electrolyte membrane and/or an electrode which includes a crosslinked polybenzoxazine-based compound formed of a polymerized product of at least one selected from a first benzoxazine-based monomer and second benzoxazine-based monomer, the first benzoxazine-based monomer and second benzoxazine-based monomer having a halogen atom or a halogen atom-containing functional group, crosslinked with a cross-linkable compound.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of Korean Patent Application No. 2007-111588, filed on Nov. 2, 2007, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Aspects of the present invention relate to an electrolyte membrane for a fuel cell and a fuel cell using the same.

2. Description of the Related Art

Fuel cells, which use a polymer electrolyte membrane as an electrolyte, operate at a relatively low temperature and can be small in size. Thus, such fuel cells are expected to be used as energy sources in electric vehicles or distributed generation systems in homes. As a polymer electrolyte membrane used in polymer electrolyte fuel cells, a perfluorocarbon sulfonic acid-based polymer membrane available as NAFION® available from E.I. du Pont de Nemours and Company is used.

However, such polymer electrolyte membranes require water in order to sufficiently conduct protons, and thus the polymer electrolyte membranes require humidification. In addition, to enhance cell system efficiencies, it is necessary to operate polymer electrolyte membranes at a high temperature, i.e., at least 100° C. However, the moisture in the polymer electrolyte membrane is evaporated at such temperatures, and polymer electrolyte membranes cannot function as a solid electrolyte.

To address such problems in the related art, non-humidified electrolyte membranes, which can operate at a high temperature of at least 100° C. without humidification, have been developed. For example, Japanese Patent Laid-Open Publication No. 11-503262 discloses a polybenzimidazole doped with a phosphoric acid, and the like, as a material for use as a non-humidified electrolyte membrane.

In addition, in cells which operate at a low temperature, such as the cells using a perfluorocarbon sulfonic acid-based polymer membrane, electrodes using polytetrafluoroethylene (PTFE) as a waterproof agent having hydrophobic properties have been widely used to prevent gas diffusion in the electrodes due to formation of water produced as electricity is generated in an electrode, particularly a cathode. For example, Japanese Patent Laid-Open Publication No. 05-283082 discloses use of such electrodes.

In addition, phosphoric acid fuel cells operating at a high temperature, i.e., 150 to 200° C., use a liquid phosphoric acid as an electrolyte. However, a large amount of the liquid phosphoric acid therein interferes with gas diffusion in the electrodes. Therefore, an electrode catalyst layer including a polytetrafluoroethylene (PTFE) as a waterproof agent, which prevents fine pores in the electrodes from being clogged by the phosphoric acid, has been used.

In addition, in fuel cells using a polybenzimidazole (PBI) electrolyte membrane, which uses a phosphoric acid as a nonhumidified electrolyte at a high temperature to reduce contact between electrodes and the electrolyte membrane, a method of impregnating the electrodes with a liquid phosphoric acid has been used and a method of increasing a loading amount of metal catalysts has been used. However, such fuel cells do not exhibit improved properties. In addition, the electrolyte membrane formed of PBI does not have satisfactory mechanical properties, chemical stability, or the capability of containing a phosphoric acid. Thus, there is still a need for improvement.

SUMMARY OF THE INVENTION

Aspects of the present invention provide a fuel cell in which an electrolyte membrane is formed of a benzoxazine-based compound having a functional group containing a halogen atom, such as fluorine, or the polymer thereof, or both an electrolyte membrane and an electrode formed of a benzoxazine-based compound having a functional group containing a halogen atom, such as fluorine, or the polymer thereof resulting in improved cell performance.

According to an aspect of the present invention, there is provided an electrolyte membrane for a fuel cell, which comprises a crosslinked polybenzoxazine-based compound formed of at least one monomer selected from a first benzoxazine-based monomer represented by Formula 1 below and a second benzoxazine-based monomer represented by Formula 2 below crosslinked with a cross-linkable compound.

According to another aspect of the present invention, there is provided a fuel cell comprising a cathode, an anode, and the electrolyte membrane for a fuel cell described above which is disposed therebetween.

According to aspects of the present invention, R₁ through R₄ are each independently hydrogen, a substituted or unsubstituted C₁-C₂₀ alkyl group, a substituted or unsubstituted C₁-C₂₀ alkoxy group, a substituted or unsubstituted C₂-C₂₀ alkenyl group, a substituted or unsubstituted C₂-C₂₀ alkynyl group, a substituted or unsubstituted C₆-C₂₀ aryl group, a substituted or unsubstituted C₆-C₂₀ aryloxy group, a substituted or unsubstituted C₂-C₂₀ heteroaryl group, a substituted or unsubstituted C₂-C₂₀ heteroaryloxy group, a substituted or unsubstituted C₄-C₂₀ cycloalkyl group, a substituted or unsubstituted C₄-C₂₀ cycloalkyloxy group, a substituted or unsubstituted C₂-C₂₀ heterocycle group, a halogen atom, a hydroxyl group, or a cyano group.

According to aspects of the present invention, R₅ is a halogenated C₁-C₂₀ alkyl group, a halogenated C₁-C₂₀ alkoxy group, a halogenated C₂-C₂₀ alkenyl group, a halogenated C₂-C₂₀ alkynyl group, a halogenated C₆-C₂₀ aryl group, a halogenated C₆-C₂₀ aryloxy group, a halogenated C₇-C₂₀ arylalkyl group, a halogenated C₂-C₂₀ heteroaryl group, a halogenated C₂-C₂₀ heteroaryloxy group, a halogenated C₂-C₂₀ heteroarylalkyl group, a halogenated C₄-C₂₀ carbocycle group, a halogenated C₄-C₂₀ carbocyclicalkyl group, a halogenated C₂-C₂₀ heterocycle group, or a halogenated C₂-C₂₀ heterocyclicalkyl group.

According to aspects of the present invention, R₅′ is a substituted or unsubstituted C₁-C₂₀ alkyl group, a substituted or unsubstituted C₁-C₂₀ alkoxy group, a substituted or unsubstituted C₂-C₂₀ alkenyl group, a substituted or unsubstituted C₂-C₂₀ alkynyl group, a substituted or unsubstituted C₆-C₂₀ aryl group, a substituted or unsubstituted C₆-C₂₀ aryloxy group, a substituted or unsubstituted C₇-C₂₀ arylalkyl group, a substituted or unsubstituted C₂-C₂₀ heteroaryl group, a substituted or unsubstituted C₂-C₂₀ heteroaryloxy group, a substituted or unsubstituted C₂-C₂₀ heteroarylalkyl group, a substituted or unsubstituted C₄-C₂₀ carbocycle group, a substituted or unsubstituted C₄-C₂₀ carbocyclicalkyl group, a substituted or unsubstituted C₂-C₂₀ heterocycle group, or a substituted or unsubstituted C₂-C₂₀ heterocyclicalkyl group.

According to aspects of the present invention, R₆ is selected from the group consisting of a substituted or unsubstituted C₁-C₂₀ alkylene group, a substituted or unsubstituted C₂-C₂₀ alkenylene group, a substituted or unsubstituted C₂-C₂₀ alkynylene group, a substituted or unsubstituted C₆-C₂₀ arylene group, a substituted or unsubstituted C₂-C₂₀ heteroarylene group, —C(═O)—, and —SO₂—,

According to aspects of the present invention, at least one of R₅′ and R₆ is a halogenated substituent.

According to aspects of the present invention, at least one of the cathode and anode may have a catalyst layer comprising a polymer of at least one selected from the first benzoxazine-based monomer of Formula 1 and the second benzoxazine-based monomer of Formula 2 and a catalyst.

Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:

FIG. 1 is a graph of voltage with respect to current density of the fuel cell of Example 1 according to aspects of the present invention;

FIG. 2 is a graph of voltage with respect to current density of the fuel cell of Example 2 according to aspects of the present invention;

FIG. 3 is a graph of voltage with respect to current density of the fuel cell of Example 3 according to aspects of the present invention;

FIG. 4 is a graph of voltage with respect to current density of the fuel cell of Example 4 according to aspects of the present invention;

FIG. 5 is a graph of voltage with respect to time of the fuel cells of Examples 1 through 3 and Comparative Example 1 according to aspects of the present invention; and

FIG. 6 is a graph of conductivity with respect to temperature of each of the fuel cells of Examples 1, 2, 3, and 5.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to the present embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain aspects of the present invention by referring to the figures. When it is stated that the electrolyte membrane includes a polymerized product of at least one monomer selected from a first and a second monomer, it is intended to refer to first monomer, the second monomer, or both the first and second monomers.

Aspects of the present invention provide an electrolyte membrane which includes a crosslinked polybenzoxazine-based compound formed of a polymerized product of at least one monomer selected from a first benzoxazine-based monomer represented by Formula 1 below and a second benzoxazine-based monomer represented by Formula 2 below crosslinked with a cross-linkable compound:

wherein R₁ through R₄ are each independently hydrogen, a substituted or unsubstituted C₁-C₂₀ alkyl group, a substituted or unsubstituted C₁-C₂₀ alkoxy group, a substituted or unsubstituted C₂-C₂₀ alkenyl group, a substituted or unsubstituted C₂-C₂₀ alkynyl group, a substituted or unsubstituted C₆-C₂₀ aryl group, a substituted or unsubstituted C₆-C₂₀ aryloxy group, a substituted or unsubstituted C₂-C₂₀ heteroaryl group, a substituted or unsubstituted C₂-C₂₀ heteroaryloxy group, a substituted or unsubstituted C₄-C₂₀ cycloalkyl group, a substituted or unsubstituted C₄-C₂₀ cycloalkyloxy group, a substituted or unsubstituted C₂-C₂₀ heterocycle group, a halogen atom, a hydroxyl group, or a cyano group.

R₅ is a halogenated C₁-C₂₀ alkyl group, a halogenated C₁-C₂₀ alkoxy group, a halogenated C₂-C₂₀ alkenyl group, a halogenated C₂-C₂₀ alkynyl group, a halogenated C₆-C₂₀ aryl group, a halogenated C₆-C₂₀ aryloxy group, a halogenated C₇-C₂₀ arylalkyl group, a halogenated C₂-C₂₀ heteroaryl group, a halogenated C₂-C₂₀ heteroaryloxy group, a halogenated C₂-C₂₀ heteroarylalkyl group, a halogenated C₄-C₂₀ carbocycle group, a halogenated C₄-C₂₀ carbocyclicalkyl group, a halogenated C₂-C₂₀ heterocycle group, or a halogenated C₂-C₂₀ heterocyclicalkyl group.

R₅′ is a substituted or unsubstituted C₁-C₂₀ alkyl group, a substituted or unsubstituted C₁-C₂₀ alkoxy group, a substituted or unsubstituted C₂-C₂₀ alkenyl group, a substituted or unsubstituted C₂-C₂₀ alkynyl group, a substituted or unsubstituted C₆-C₂₀ aryl group, a substituted or unsubstituted C₆-C₂₀ aryloxy group, a substituted or unsubstituted C₇-C₂₀ arylalkyl group, a substituted or unsubstituted C₂-C₂₀ heteroaryl group, a substituted or unsubstituted C₂-C₂₀ heteroaryloxy group, a substituted or unsubstituted C₂-C₂₀ heteroarylalkyl group, a substituted or unsubstituted C₄-C₂₀ carbocycle group, a substituted or unsubstituted C₄-C₂₀ carbocyclicalkyl group, a substituted or unsubstituted C₂-C₂₀ heterocycle group, or a substituted or unsubstituted C₂-C₂₀ heterocyclicalkyl group.

R₆ is selected from the group consisting of a substituted or unsubstituted C₁-C₂₀ alkylene group, a substituted or unsubstituted C₂-C₂₀ alkenylene group, a substituted or unsubstituted C₂-C₂₀ alkynylene group, a substituted or unsubstituted C₆-C₂₀ arylene group, a substituted or unsubstituted C₂-C₂₀ heteroarylene group, —C(═O)—, and —SO₂—.

Further, according to aspects of the present invention, at least one of R₅′ and R₆ is a halogenated substituent.

The cross-linkable compound used may be at least one selected from polybenzimidazoles (PBI), a polybenzimidazole-base complex, polybenzthiazoles, polybenzoxazoles, and polyimides.

When the cross-linkable compound is PBI or the polybenzimidazole-base complex, an electrolyte membrane according to an embodiment of the present invention comprises a crosslinked polybenzoxazine-based compound formed of a polymerized product of polybenzoxazine together with PBI or the polybenzimidazole-base complex.

The electrolyte membrane having the above-described composition reduces problems caused when an electrolyte membrane formed of polybenzimidazole alone is used, such as, a pin-hole phenomenon caused by mechanical and chemical instability at a high temperature of the electrolyte membrane including only polybenzimidazole. In addition to this, when the electrode comprises, as described above, a halogen-containing benzoxazine-based monomer, particularly, the polymer of a fluorine-containing benzoxazine-based monomer, the transmission of oxygen into the electrode is increased, and thus the amount of oxygen dissolved in the electrode is increased, resulting in a reduction in the activation time of the electrode. In particular, when R₅ is a fluorine-substituted phenyl group, the advantages of a fluorine-containing polymer, such as excellent oxygen transmission, thermal resistance, and resistance to phosphoric acid can be obtained, and the compatibility of three-phases, that is, gas phase (fuel gas or oxidized gas)-liquid phase (phosphoric acid)-solid phase (catalyst) can be enhanced.

Aspects of the present invention also provide a fuel cell including an electrode which comprises a catalyst and a polymer of at least one selected from the first benzoxazine-based monomer of Formula 1 and the second benzoxazine-based monomer of Formula 2.

In Formula 1, R₅ may be a fluorinated functional group, and may be one of the groups represented by following formulae:

In Formula 1, R₁ through R₄ may be each independently hydrogen, F, a C₁-C₁₀ alkyl group, an allyl group, or a C₆-C₁₀ aryl group. In addition, in Formula 2, R₆ may be —C(CF₃)₂—, —SO₂—, or —C(CH₃)₂—, and R₅′ may be a phenyl group, and may be one of the same groups as the fluorinated functional groups of R₅ described above represented by the following formulae:

As described above, in Formula 2, at least one of R₅′ and R₆ may be a halogenated substituent, and may be a fluorinated substituent.

The first benzoxazine-based monomer of Formula 1 may be a compound represented by Formula 3 or 4 below.

In addition, the second benzoxazine-based monomer of Formula 2 may be a compound represented by Formula 5 below.

The fuel cell according to aspects of the present invention includes an electrolyte membrane formed of an optimized material or includes an electrolyte membrane and electrode formed of optimized materials, thereby exhibiting improved cell performance.

In the electrode according to aspects of the present invention, the amount of the at least one polymer selected from the first benzoxazine-based monomer of Formula 1 and the second benzoxazine-based monomer of Formula 2 may be in the range of 0.1 to 50 parts by weight based on 100 parts by weight of the catalyst.

When the amount of the polymer of at least one selected from the first benzoxazine-based monomer of Formula 1 and the second benzoxazine-based monomer of Formula 2 is less than 0.1 parts by weight based on 100 parts by weight of the catalyst, the effect of an additive or binder is insignificant. On the other hand, when the amount of the polymer of at least one selected from the first benzoxazine-based monomer of Formula 1 and the second benzoxazine-based monomer of Formula 2 is greater than 50 parts by weight based on 100 parts by weight of the catalyst, an interfacial resistance is increased.

The catalyst may be platinum alone, or an alloy or mixture of platinum and at least one metal selected from the group consisting of gold, palladium, rhodium, iridium, ruthenium, tin, molybdenum, cobalt, and chrome.

The electrode may further include a binder which can be conventionally used in the preparation of an electrode for a fuel cell.

The binder may be at least one selected from the group consisting of poly(vinylidenefluoride), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoroethylene copolymer, fluorinated ethylene propylene (FEP), styrene butadiene rubber (SBR), and polyurethane. The amount of the binder may be in the range of 0.1 to 50 parts by weight based on 100 parts by weight of the catalyst. When the amount of the binder is less than 0.1 parts by weight based on 100 parts by weight of the catalyst, the adhesion between electrodes is poor such that it is difficult to maintain the shape of a catalyst layer. On the other hand, when the amount of the binder is greater than 50 parts by weight based on 100 parts by weight of the catalyst, an electric resistance in the electrode is increased.

The polybenzimidazole-base complex which can be used herein as the cross-linkable compound is the compound disclosed in Korean Patent No. 2007-102579 filed by the present applicant. The polybenzimidazole-base complex is produced by reacting a polybenzimidazole solution in which a polybenzimidazole-based material is dissolved in an organic solvent with a base, and then heat treating the resultant.

The base may be a weak base, and may be at least one carbonate selected from the group consisting of sodium carbonate (Na₂CO₃), sodium hydrogen carbonate (NaHCO₃), potassium carbonate (K₂CO₃), potassium hydrogen carbonate (KHCO₃), lithium carbonate (Li₂CO₃), rubidium carbonate (Rb₂CO₃), cesium carbonate (Cs₂CO₃), ammonium carbonate ((NH₄)₂CO₃), and ammonium hydrogen carbonate ((NH₄)HCO₃). The amount of the base may be in the range of 0.01 to 20 parts by weight based on 100 parts by weight of the polybenzimidazole-based material.

When the amount of the base is less than 0.01 parts by weight based on 100 parts by weight of the polybenzimidazole-based material, the polybenzimidazole-base complex is not completely formed. On the other hand, when the amount of the base is greater than 20 parts by weight based on 100 parts by weight of the polybenzimidazole-based material, the viscosity of the base is increased, and thus the base may not be uniformly dispersed in the complex.

The polybenzimidazole-based material may be poly[2,2′-(m-phenylene)-5,5′-bibenzimidazole] (PBI) or poly(2,5-benzimidazole) (ABPBI).

The formation of the polybenzimidazole-base complex can be confirmed through nuclear magnetic resonance spectrometry (NMR). An analyzer used in an NMR analysis is a Bruker NMR 300 MHz (model name: DPX 300) commercially available from Bruker Biospin. The NMR analysis was performed using a sample, 0.8 ml of a resultant solution prepared by dissolving 10 mg of the polybenzimidazole-base complex in 0.7 mL of DMSO-d6. In addition, a thermogravimetric analysis (TGA) is performed using a TGA 2050 commercially available from TA Instruments, performed at a temperature in the range of room temperature to 1000° C. (10° C./min), and performed using a Pt pan under a nitrogen (N₂) gas atmosphere.

The thermal decomposition initiation temperature of the polybenzimidazole-base complex prepared by the above-described preparation process may be in the range of 180 to 220° C., and preferably about 200° C. In addition, the thermal decomposition rate of the polybenzimidazole-base complex at a heating temperature of 20 to 1000° C. may be in the range of 8 to 15° C./min, and preferably about 10° C./min, and a 10% weight loss temperature in the TGA curve is in the range of 200 to 280° C., and particularly about 250° C.

The thermal decomposition initiation temperature, thermal decomposition rate, and 10% weight loss temperature in the TGA curve are measured using the TGA analyzer (TGA 2050) available from TA Instruments, and measured at a heating rate of 8 to 15° C./min, particularly 10° C./min under a nitrogen gas atmosphere.

The polybenzimidazole-base complex may have a ratio of weight average molecular weight to number average molecular weight (M_(w)/M_(n), referred to as “molecular weight distribution”) of 2.1 to 2.5, and preferably about 2.4. The polybenzimidazole-base complex has a weight average molecular weight of 65,000 to 70,000, preferably about 69,000, has a number average molecular weight of 25,000 to 30,000, preferably about 29,000, and has a viscosity average molecular weight of 80,000 to 83,000, preferably about 82,000.

The weight average molecular weight, number average molecular weight, and viscosity average molecular weight are measured by a gel permeation chromatography (GPC) method. An analyzer used in the measurement of the molecular weights is the TDA 302 available from Viscotek GPCmax. In the GPC analysis, an eluent is dimethylformamide (DMF) and 0.1 wt % of LiBr, a column is PLGel Mixed-C*2 (temp: 40° C.), a flow rate is about 1 ml/min, and an injection volume is about 100 μl.

In addition, the polybenzimidazole-base complex does not have a peak corresponding to a peak of NH of imidazole of a general polybenzimidazole-based material, at a chemical shift of 12 to 15 ppm, which was determined using ¹H nuclear magnetic resonance (¹H-NMR) spectrometry. A peak is detected at a chemical shift of 9.15±0.5 (s, 1 H), 8.30±0.5 (d, 2H), 7.92±0.5 (s, 1H), 7.75±0.5 (m, 3H), and 7.62±0.5 (m, 3H) using ¹H-NMR operating at 300 MHz. Using ¹H-NMR operating at 300 MHz, it can be seen that an NH peak at a chemical shift of 12 to 15 ppm, particularly around about 14 ppm, which is apparent before the formation of the polybenzimidazole-base complex, disappears, and simultaneously, peaks of polybenzimidazole are accurately split in the range of 8.2 to 7.4 ppm to correspond to integration values.

The NH peak at a chemical shift of 12 to 15 ppm, particularly around about 14 ppm, disappears in the polybenzimidazole-based material because that the polybenzimidazole-based material reacts with the base, and while the resultant is heat treated, —NH— of polybenzimidazole participates in the reaction, thereby changing the magnetic characteristics in an environment surrounding H. In the NMR analysis, a solvent used for dissolving the polybenzimidazole-base complex may be DMSO-d6, DMF-d6, or the like, and preferably DMSO-d6.

A device used in the NMR analysis is the DPX 300 available from Bruker Biospin, and a solvent used in the NMR analysis for dissolving the polybenzimidazole-base complex is DMSO-d6.

The amount of a metal ion (for example, Na⁺, K⁺, Ca²⁺, and the like) measured by inductively coupled plasma (ICP) analysis of the polybenzimidazole-base complex may be in the range of 300 to 1,200 ppm, and preferably in the range of 323 to 1,170 ppm. A device used in the ICP analysis is the ICPS-8100 sequential spectrometer available from Shimadzu.

The amount of the cross-linkable compound used in the preparation of the electrolyte membrane according to aspects of the present invention may be in the range of 5 to 95 parts by weight based on 100 parts by weight of the at least one polymer selected from the first benzoxazine-based monomer and the second benzoxazine-based monomer.

When the amount of the cross-linkable compound is less than 5 parts by weight based on 100 parts by weight of the at least one polymer selected from the first benzoxazine-based monomer and the second benzoxazine-based monomer, the electrolyte membrane is not impregnated with a phosphoric acid, and thus, proton conductivity of the electrolyte membrane is reduced. On the other hand, when the amount of the cross-linkable compound is greater than 95 parts by weight based on 100 parts by weight of the at least one polymer selected from the first benzoxazine-based monomer and the second benzoxazine-based monomer, the crosslinking agent is dissolved in polyphosphoric acid due to the presence of excessive phosphoric acid so that gas permeation occurs.

The C₁-C₂₀ alkyl group used herein may be methyl, ethyl, propyl, isobutyl, sec-butyl, pentyl, iso-amyl, hexyl, or the like. At least one hydrogen atom of the alkyl group may be substituted with a halogen atom, a C₁-C₂₀ alkyl group substituted with a halogen atom (for example, CCF₃, CHCF₂, CH₂F, CCl₃, and the like), a hydroxyl group, a nitro group, a cyano group, an amino group, an amidino group, hydrazine, hydrazone, a carboxyl group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid or a salt thereof, a C₁-C₂₀ alkyl group, a C₂-C₂₀ alkenyl group, a C₂-C₂₀ alkynyl group, a C₁-C₂₀ heteroalkyl group, a C₆-C₂₀ aryl group, a C₆-C₂₀ arylalkyl group, a C₆-C₂₀ heteroaryl group, a C₁-C₂₀ heterocycle group, or a C₆-C₂₀ heteroarylalkyl group.

The aryl group used herein is used alone or in combination, and refers to a C₆-C₂₀ carbocyclic aromatic system containing at least one ring, wherein the rings can be attached to each other using a pedant method or fused with each other. The term “aryl” refers to an aromatic radical, including phenyl, naphthyl, tetrahydronaphthyl, or the like. At least one hydrogen atom of the aryl group may be substituted with the same substituent as in the alkyl group described above.

The aryloxy group used herein may be a phenoxy group, a naphthyloxy group, a tetrahydronaphthyloxy group, or the like. At least one hydrogen atom of the aryloxy group may be substituted with the same substituent as in the alkyl group described above.

The heteroaryl group used herein refers to a monovalent, monocyclic, or bicyclic aromatic bivalent organic compound which contains 1, 2 or 3 heteroatoms selected from the group consisting of N, O, P, and S and has 1 to 20 carbon atoms. The heteroaryl may be pyrazinyl, furanyl, thienyl, pyridyl, pyrimidinyl, isothiazolyl, oxazolyl, thiazolyl, triazolyl, 1,2,4-thiadiazolyl, or the like. At least one hydrogen atom of the heteroaryl group may be substituted with the same substituent as in the alkyl group described above. In addition, the halogenated heteroaryl group used herein refers to a heteroaryl group substituted with a heteroatom such as fluorine, chlorine, and the like.

The heteroaryloxy group used herein may be pyrazinyloxy, furanyloxy, thienyloxy, pyridyloxy, pyrimidinyloxy, isothiazolyloxy, oxazolyloxy, thiazolyloxy, triazolyloxy, 1,2,4-thiadiazolyloxy, or the like. At least one hydrogen atom of the heteroaryloxy group may be substituted with the same substituent as in the alkyl group described above. The halogenated heteroaryloxy group used herein refers to a heteroaryloxy group substituted with a hetero atom such as fluorine, chlorine, and the like.

The heterocycle group used herein refers to a 5 to 10 membered ring group containing a heteroatom such as nitrogen, sulfur, phosphorus, oxygen, and the like. At least one hydrogen atom of the heterocycle group may be substituted with the same substituent as in the alkyl group described above. In addition, the halogenated heterocycle group used herein refers to a heterocycle group substituted with a hetero atom such as fluorine, chlorine, and the like.

The cycloalkyl group used herein may be a cyclohexyl group, a cyclopentyl group, or the like. At least one hydrogen atom of the cycloalkyl group may be substituted with the same substituent as in the alkyl group described above. In addition, the halogenated cycloalkyl group used herein refers to a cycloalkyl group substituted with a hetero atom such as fluorine, chlorine, and the like.

Hereinafter, a method of preparing a fuel cell according to an embodiment of the present invention will be described. First, a method of preparing an electrode is as follows:

First, a catalyst is dispersed in a solvent to obtain a dispersion. The solvent used is N-methylpyrolidone (NMP), dimethylformamide (DMAc), or the like, and the amount of the solvent is in the range of 100 to 1,000 parts by weight based on 100 parts by weight of the catalyst.

A mixture of a solvent and at least one selected from the first benzoxazine-based monomer of Formula 1 and the second benzoxazine-based monomer of Formula 2 is added to the dispersion and mixed together, and then the resultant is stirred. The mixture may further include a binder. The solvent is N-methylpyrolidone (NMP), dimethylacetamide (DMAc), or the like.

The resultant is coated on the surface of a carbon support to prepare an electrode. Herein, the carbon support may be fixed on a glass substrate in order to easily coat the resultant thereon. The coating method is not particularly limited, but, may be coated using a doctor blade, bar coating, screen printing, or the like.

The coated resultant is dried at a temperature in the range of 20 to 150° C., wherein the drying process is performed to remove the solvent. The drying time is dependent upon the drying temperature, and is in the range of 10 to 60 minutes.

As can be seen in the method of preparing an electrode described above, the electrode for a fuel cell, which is finally obtained, contains a polymer of at least one selected from the first benzoxazine-based monomer of Formula 1 and the second benzoxazine-based monomer of Formula 2. Herein, at least one selected from the first benzoxazine-based monomer of Formula 1 and the second benzoxazine-based monomer of Formula 2 is polymerized during the drying process described above and/or while a fuel cell including the electrode operates, thereby being converted to a polymer thereof.

Next, a method of preparing an electrolyte membrane according to an embodiment of the present invention is as follows:

A method of preparing an electrolyte membrane using polybenzimidazole as a cross-linkable compound will be described.

As a first method, at least one selected from the first benzoxazine-based monomer of Formula 1 and the second benzoxazine-based monomer of Formula 2 described above and the cross-linkable compound such as PBI or a PBI-base complex are blended, and then the mixture is hardened at a temperature in the range of 50 to 250° C., and particularly in the range of 80 to 220° C. Subsequently, the resultant is impregnated with a proton conductor, such as an acid, to form an electrolyte membrane.

As a second method, at least one selected from the first benzoxazine-based monomer of Formula 1 and the second benzoxazine-based monomer of Formula 2 and the cross-linkable compound such as PBI or a PBI-base complex are mixed together. Using the mixture, an electrolyte membrane is formed.

The formation of the electrolyte membrane may be performed by a tape casting method, or a conventional coating method. The conventional coating method may be a method in which the mixture is cast on a support using a doctor blade. Herein, a doctor blade with a 250 to 500 μm gap is used. When the casting method using a doctor blade is used, the process of forming the electrolyte membrane further includes separating the electrolyte membrane from the support, between the time when hardening of the mixture occurs and the time when impregnation of the resultant with acid occurs. When it is time to perform the process of separating the electrolyte membrane from the support, the mixture is immersed in distilled water with a temperature in the range of 60 to 80° C.

The support can be any support which can support an electrolyte membrane, for example, a glass substrate, a polyimide film, and the like. When the tape casting method is used, a tape cast membrane is separated on a support such as polyethyleneterephthalate before being hardened, and then put into an oven. In addition, when a membrane is formed by the tape casting method using a mixture of a benzoxazine-based monomer and polybenzimidazole, a process of filtering the mixture may be further performed. The tape cast membrane is hardened by heat treatment, and then impregnated with a proton conductor, such as an acid, to form an electrolyte membrane.

Nonrestrictive examples of the proton conductor include a phosphoric acid, a C₁-C₁₀ alkyl phosphonic acid, and the like. The C₁-C₁₀ alkyl phosphonic acid may be ethyl phosphonic acid, and the like. The amount of the proton conductor is in the range of 300 to 1,000 parts by weight based on 100 parts by weight of the total weight of the electrolyte membrane. The concentration of the acid used is not particularly limited. However, in the case of a phosphoric acid, 85 wt % of an aqueous phosphoric acid solution is used, and the impregnation time of the phosphoric acid is in the range of 2.5 to 14 hours at 80° C.

A method of manufacturing a membrane-electrode assembly for a fuel cell, according to aspects of the present invention, is as follows. The term “membrane and electrode assembly (MEA)” used herein refers to a structure in which an electrolyte membrane is disposed between two electrodes, each electrode comprising a catalyst layer and a diffusion layer. The MEA may be formed by positioning the electrode including the catalyst layer for an electrode described above at both sides of the electrolyte membrane, joining them all together at a high temperature and under a high pressure, and then joining a fuel diffusion layer to the catalyst layers. Herein, the joining is performed under a pressure in the range of 0.1 to 3 ton/cm², and particularly about 1 ton/cm², in a state reached when the MEA is heated up to a temperature that softens the electrolyte membrane.

Next, a bipolar plate is disposed on each side of the membrane-electrode assembly to manufacture a fuel cell. The bipolar plate has grooves used for supplying fuel and functions as a current collector. However, the fuel cell is not limited thereto such that a monopolar plate may be disposed on at least one side of the membrane-electrode assembly as needed.

The use of the fuel cell according to aspects of the present invention is not particularly limited. However, the fuel cell may be used as a polymer electrolyte membrane (PEM) fuel cell.

Hereinafter, aspects of the present invention will be described more specifically with reference to the following examples. The following examples are only for illustrative purposes and are not intended to limit the scope of the invention.

SYNTHESIS EXAMPLE 1 Preparation of tBuPh-4FA of Formula 3

1 mol of tertiary butylphenol, 2.2 mol of p-formaldehyde, and 1.1 mol of 4-fluoroaniline were mixed together, and the mixture was stirred at 100° C. for 1 hour without a solvent to obtain a crude product. The crude product was sequentially washed with an aqueous 1N NaOH solution twice and with distilled water once, and then dried using magnesium sulfate. Subsequently, the resultant was filtered and then the solvent was removed therefrom. Then, the resultant was dried under vacuum to obtain tBuPh-4FA of Formula 3 with a yield of 95%. The structure of the obtained compound was confirmed through NMR spectrometry.

SYNTHESIS EXAMPLE 2 Preparation of 4FPh-246TFA of Formula 4

1 mol of 4-fluorophenol, 2.2 mol of p-formaldehyde, and 1.1 mol of 2,4,6-trifluoroaniline were mixed together, and the mixture was stirred at 100° C. for 1 hour without a solvent to obtain a crude product. The crude product was sequentially washed with an aqueous 1N NaOH solution twice and with distilled water once, and then dried using magnesium sulfate. Subsequently, the resultant was filtered and then the solvent was removed therefrom. Then, the resultant was dried under vacuum to obtain 4FPh-246TFA of Formula 4 with a yield of 95%. The structure of the obtained compound was confirmed through NMR spectrometry.

SYNTHESIS EXAMPLE 3 Preparation of poly[2,2′-(m-phenylene)-5,5′-bibenzimidazole] (PBI)

4.84 g of 3,3′-diaminobenzidine (22.6 mmol) and 3.76 g of isophthalic acid (22.6 mmol) were dissolved in a mixed solution of 8 g of P₂O₅, 30 ml of CF₃SO₃H, and 30 ml of CH₃SO₃H. The reaction mixture was reacted at 150° C. for 30 minutes under a nitrogen atmosphere. The more the reaction proceeded, the more the reaction mixture was changed to a homogeneous solution and the more the viscosity thereof was increased. To obtain polymer in the form of fine powder, a polymer solution that was still hot was poured into about 1.5 L of water using a peristaltic pump. The produced powder was washed using water several times, and the residue phosphoric acid in the polymer was filtered using a 10% ammonium hydroxide solution and a Soxhlet device until phosphorous residue was not confirmed present by elemental analysis. Next, the obtained polymer was dried under pressure at 50° C. for 3 days to obtain about 6 g of polymer (poly[2,2′-(m-phenylene)-5,5′-bibenzimidazole] (PBI)). The obtained PBI was precipitated using methanol, and the formed precipitate was washed with methanol to obtain PBI.

SYNTHESIS EXAMPLE 4 Preparation of Polybenzimidazole-Base Complex

50 g of dimethylacetamide was added to 5 g of the PBI powder prepared by Synthesis Example 3 to obtain 10 wt % of a PBI solution. 0.5 g of sodium carbonate was added to the PBI solution, and then the mixture was stirred at 80° C. for over 1 hour. Subsequently, the resultant was filtered to obtain a polybenzimidazole-base complex.

SYNTHESIS EXAMPLE 5 Preparation of HFa Represented by Formula 5

1 mol of 4,4′-hexafluoroisopropylidene diphenol (4,4′-HFIDPH), 4.4 mol of p-formaldehyde, and 2.2 mol of benzene were mixed together, and the mixture was stirred at 100° C. for 1 hour without a solvent to obtain a crude product. The crude product was sequentially washed with an aqueous 1N NaOH solution twice and with distilled water once and then dried using magnesium sulfate. Subsequently, the resultant was filtered and then the solvent was removed therefrom. Then, the resultant was dried under vacuum to obtain a benzoxazine-based monomer of Formula 5 where R₂ is a phenyl group with a yield of 96%. The structure of the obtained HFa was confirmed through NMR spectrometry.

EXAMPLE 1 Preparation of Fuel Cell

1 g of a catalyst in which 50 wt % of PtCo was supported on carbon and 3 g of NMP were added in a stirrer, and the mixture was stirred using a mortar to prepare a slurry. A NMP solution of tBuPh-4FA of Synthesis Example 1 was added to the slurry to make the resultant contain 0.025 g of tBuPh-4FA. The resultant was further stirred.

Subsequently, an N-methylpyrolidone (NMP) solution of 5 wt % of polyvinylidene fluoride was added to the resultant to make the resultant contain 0.025 g of polyvinylidene fluoride. The resultant was mixed for 10 minutes to prepare a slurry used for forming a cathode catalyst layer.

Carbon paper was cut to a size of 4×7 cm, fixed on a glass plate, and coated by a doctor blade (Sheen instrument). Herein, a gap interval was adjusted to 600 μm.

The slurry used for forming a cathode catalyst layer was coated on the carbon paper, and the resultant was dried at room temperature for 1 hour, dried at 80° C. for 1 hour, dried at 120° C. for 30 minutes, and dried at 150° C. for 15 minutes to prepare a cathode. The loading amount of PtCo in the prepared cathode was 2.32 mg/cm².

An electrode prepared by the following processes was used as an anode. 2 g of a catalyst in which 50 wt % of Pt was supported on carbon and 9 g of NMP were added to a stirrer, and the mixture was stirred for 2 minutes using a high speed stirrer.

Subsequently, a solution in which 0.05 g of polyvinylidene fluoride was dissolved in 1 g of NMP was added to the mixture, and the resultant was further stirred for 2 minutes to prepare a slurry used for forming an anode catalyst layer. The slurry used for forming an anode catalyst layer was coated on carbon paper coated with a microporous layer using a bar coater. As a result, preparation of the anode was completed. The loading amount of Pt in the prepared anode was 1.44 mg/cm².

Separately, 65 parts by weight of tBuPh-4FA of Formula 3 prepared by Synthesis Example 1 and 35 parts by weight of polybenzimidazole of Synthesis Example 3 were blended together, and then the mixture was cured at about 220° C. Subsequently, the resultant was impregnated with 85 wt % of phosphoric acid at 80° C. for over 4 hours to form an electrolyte membrane. Herein, the amount of phosphoric acid was about 459 parts by weight based on 100 parts by weight of the total weight of the electrolyte membrane.

The electrolyte membrane was disposed between the cathode and the anode to prepare an MEA. The cathode and anode were not impregnated with phosphoric acid.

To prevent gas permeation between the cathode and the anode, a TEFLON® membrane for a main gasket with a thickness of 200 μm and a TEFLON® membrane for a subgasket with a thickness of 20 μm were joined and disposed between the electrode and the electrolyte membrane.

Electricity was generated by causing hydrogen to flow into the anode (flowrate: 100 ccm) and causing air to flow into the cathode (flowrate: 250 ccm) at 150° C. under a condition where the electrolyte membrane was not humidified, and properties of the fuel cell prepared were measured. Herein, an electrolyte doped with a phosphoric acid was used, and thus the performance of the fuel cell improved as time elapsed. Thus, aging was performed until an operating voltage reached a peak, and then the properties of the fuel cell were finally evaluated. In addition, the area of the cathode and anode was fixed to a size of 2.8×2.8 (7.84 cm²), and the thickness of the cathode was about 430 μm and the thickness of the anode was about 390 μm.

Voltage with respect to current density and time of aging of the fuel cell manufactured by Example 1 was measured. The results are shown in FIG. 1. In FIG. 1, d1 denotes a 1 day aging, d3 denotes a 3 day aging, d5 denotes a 5 day aging, and d7 denotes a 7 day aging. Referring to FIG. 1, it can be seen that the activation time was small, and the electrolyte membrane containing a large amount of a fluorine substituent exhibited a good cell voltage, i.e., 0.689 V @ 0.3 A/cm².

EXAMPLE 2 Manufacturing of a Fuel Cell

A cathode was prepared in the same manner as in Example 1, except that 2.5 parts by weight of 4FPh-246TFA of Formula 4 prepared by Synthesis Example 2 was used instead of tBuPh-4FA used in the preparation of the cathode, and the loading amount of PtCo in the completed cathode was 2.89 mg/cm². An anode was prepared in the same manner as in Example 1.

An electrolyte membrane was prepared in the same manner as in Example 1, except that 65 parts by weight of tBuPh-4FA of Formula 3 prepared by Synthesis Example 1 and 35 parts by weight of the polybenzimidazole-base complex of Synthesis Example 4 were used as the material for forming an electrolyte membrane, instead of 65 parts by weight of tBuPh-4FA of Formula 3 prepared by Synthesis Example 1 and 35 parts by weight of polybenzimidazole of Synthesis Example 3, and the amount of the phosphoric acid was about 550 parts by weight based on 100 parts by weight of the total weight of the electrolyte membrane.

A fuel cell was manufactured in the same manner as in Example 1 by using the cathode, anode, and electrolyte membrane.

Voltage with respect to current density and time of aging of the fuel cell manufactured by Example 2 was measured. The results are shown in FIG. 2. In FIG. 2, d1 denotes a 1 day aging, d3 denotes a 3 day aging, d5 denotes a 5 day aging, and d7 denotes a 7 day aging. Referring to FIG. 2, it can be seen that activation time was small, and the electrolyte membrane containing a large amount of a fluorine substituent exhibited a good cell voltage, i.e., 0.689 V @ 0.3 A/cm². In addition, it can be seen that in the case of the electrolyte membrane comprising the PBI complex, there is no flooding of the electrodes in spite of the high impregnation rate.

EXAMPLE 3 Manufacture of Fuel Cell

A cathode was prepared in the same manner as in Example 1, except that a vinylidene fluoride-hexafluoropropylene copolymer was used instead of polyvinylidene fluoride and 2.5 parts by weight of 4FPh-246TFA of Formula 4 prepared by Synthesis Example 2 was used instead of tBuPh-4FA used in the preparation of the cathode, and the loading amount of PtCo in the completed cathode was 3.1005 mg/cm².

An anode was prepared in the same manner as in Example 1, except that the loading amount of Pt in the completed anode was 1.522 mg/cm².

An electrolyte membrane was prepared in the same manner as in Example 1, except that 60 parts by weight of tBuPh-4FA of Formula 3 prepared by Synthesis Example 1, 3 parts by weight of HFa of Formula 5 of Synthesis Example 5, and 37 parts by weight of polybenzimidazole prepared by Synthesis Example 3 were used as the material for forming an electrolyte membrane, instead of 65 parts by weight of tBuPh-4FA of Formula 3 prepared by Synthesis Example 1 and 35 parts by weight of polybenzimidazole, and the amount of the phosphoric acid was about 544 parts by weight based on 100 parts by weight of the total weight of the electrolyte membrane.

A fuel cell was manufactured in the same manner as in Example 1 by using the cathode, anode, and electrolyte membrane.

Voltage with respect to current density and time of aging of the fuel cell manufactured by Example 3, was measured. The results are shown in FIG. 3. In FIG. 3, d1 denotes a 1 day aging, d3 denotes a 3 day aging, d5 denotes a 5 day aging, and d7 denotes a 7 day aging. Referring to FIG. 3, it can be seen that activation time was small, and the electrolyte membrane containing a large amount of a fluorine substituent exhibited a good cell voltage, i.e., 0.698 V @ 0.3 A/cm².

EXAMPLE 4 Manufacturing of a Fuel Cell

A cathode was prepared in the same manner as in Example 1, except that 2.5 parts by weight of 4FPh-246TFA of Formula 4 prepared by Synthesis Example 2 was used instead of tBuPh-4FA used in the preparation of the cathode, and the loading amount of PtCo in the completed cathode was 3.1005 mg/cm².

An anode was prepared in the same manner as in Example 1.

An electrolyte membrane was prepared in the same manner as in Example 1, except that 60 parts by weight of tBuPh-4FA, 3 parts by weight of HFa of Formula 5 of Synthesis Example 5, and 37 parts by weight of polybenzimidazole prepared by Synthesis Example 3 were used as the material for forming an electrolyte membrane, instead of 65 parts by weight of tBuPh-4FA and 35 parts by weight of polybenzimidazole of Synthesis Example 3, and the amount of the phosphoric acid was about 544 parts by weight based on 100 parts by weight of the total weight of the electrolyte membrane.

A fuel cell was manufactured in the same manner as in Example 1 by using the cathode, anode, and electrolyte membrane.

Voltage with respect to current density and time of aging of the fuel cell manufactured by Example 4 was measured. The results are shown in FIG. 4. In FIG. 4, d1 denotes a 1 day aging, d3 denotes a 3 day aging, d5 denotes a 5 day aging, and d7 denotes a 7 day aging. Referring to FIG. 4, it can be seen that activation time was small, and the electrolyte membrane containing a large amount of a fluorine substituent exhibited good cell voltage, i.e., 0.700 V @ 0.3 A/cm². In addition, it can be seen that in the case of the electrolyte membrane comprising the PBI complex, there is no flooding of the electrodes in spite of the high impregnation rate.

EXAMPLE 5 Manufacturing of a Fuel Cell

A cathode was prepared in the same manner as in Example 1, except that 2.5 parts by weight of 4FPh-246TFA of Formula 4 prepared by Synthesis Example 2 was used instead of tBuPh-4FA used in the preparation of the cathode, and the loading amount of PtCo in the completed cathode was 3.1005 mg/cm².

An anode was prepared in the same manner as in Example 1.

An electrolyte membrane was prepared in the same manner as in Example 1, except that 60 parts by weight of tBuPh-4FA, 3 parts by weight of HFa of Formula 5 of Synthesis Example 5, and 37 parts by weight of the polybenzimidazole-base complex prepared by Synthesis Example 4 were used as the material for forming an electrolyte membrane, instead of 65 parts by weight of tBuPh-4FA and 35 parts by weight of polybenzimidazole of Synthesis Example 3, and the amount of the phosphoric acid was about 544 parts by weight based on 100 parts by weight of the total weight of the electrolyte membrane.

A fuel cell was manufactured in the same manner as in Example 1 by using the cathode, anode and electrolyte membrane.

COMPARATIVE EXAMPLE 1 Manufacturing of a Fuel Cell

A cathode was prepared in the same manner as in Example 1, except that the electrolyte membrane was formed of polybenzimidazole, not by using 4FPh-246TFA of Formula 4 in the preparation of the cathode, and a fuel cell using the cathode was manufactured in the same manner as in Example 2.

Voltage with respect to time of the fuel cells of Examples 1 through 3 and Comparative Example 1 was measured. The results are shown in FIG. 5. In FIG. 5, FB14FA represents Example 1, FB24FA represents Example 2, FT1w246TFA represents Example 3, and T1represents Comparative Example. Referring to FIG. 5, it can be seen that the fuel cells of Examples 1 through 3 exhibit improved voltage performance through fast activation compared to that of the fuel cell of Comparative Example 1.

Conductivity with respect to temperature of each of the electrolyte membranes prepared by Example 1, Example 2, Example 3, and Example 5 was measured. The results are shown in FIG. 6. In FIG. 6, FT1-4FA represents the electrolyte membrane of Example 3, FT2-4FA represents the electrolyte membrane of Example 5, FB1-4FA represents the electrolyte membrane of Example 1, and FB2-4FA represents the electrolyte membrane of Example 2. Referring to FIG. 6, it can be seen that each of the electrolyte membranes of Examples 1, 2, 3 and 5 has excellent ionic conductivity.

In addition, a mechanical property and resistance to a phosphoric acid of each of the electrolyte membranes of Examples 1, 2, 3 and 5 were evaluated. As a result of the evaluation, it can be confirmed that the electrolyte membranes of Examples 1, 2, 3 and 5 have excellent mechanical properties and impregnation capability with respect to the phosphoric acid and also have good resistance to the phosphoric acid.

Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in this embodiment without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents. 

1. An electrolyte membrane for a fuel cell, which comprises a crosslinked polybenzoxazine-based compound formed at least one monomer selected from a first benzoxazine-based monomer represented by Formula 1 below and a second benzoxazine-based monomer represented by Formula 2 below crosslinked with a cross-linkable compound,

wherein R₁ through R₄ are each independently hydrogen, a substituted or unsubstituted C₁-C₂₀ alkyl group, a substituted or unsubstituted C₁-C₂₀ alkoxy group, a substituted or unsubstituted C₂-C₂₀ alkenyl group, a substituted or unsubstituted C₂-C₂₀ alkynyl group, a substituted or unsubstituted C₆-C₂₀ aryl group, a substituted or unsubstituted C₆-C₂₀ aryloxy group, a substituted or unsubstituted C₂-C₂₀ heteroaryl group, a substituted or unsubstituted C₂-C₂₀ heteroaryloxy group, a substituted or unsubstituted C₄-C₂₀ cycloalkyl group, a substituted or unsubstituted C₄-C₂₀ cycloalkyloxy group, a substituted or unsubstituted C₂-C₂₀ heterocycle group, a halogen atom, a hydroxyl group, or a cyano group, R₅ is a halogenated C₁-C₂₀ alkyl group, a halogenated C₁-C₂₀ alkoxy group, a halogenated C₂-C₂₀ alkenyl group, a halogenated C₂-C₂₀ alkynyl group, a halogenated C₆-C₂₀ aryl group, a halogenated C₆-C₂₀ aryloxy group, a halogenated C₇-C₂₀ arylalkyl group, a halogenated C₂-C₂₀ heteroaryl group, a halogenated C₂-C₂₀ heteroaryloxy group, a halogenated C₂-C₂₀ heteroarylalkyl group, a halogenated C₄-C₂₀ carbocycle group, a halogenated C₄-C₂₀ carbocyclicalkyl group, a halogenated C₂-C₂₀ heterocycle group, or a halogenated C₂-C₂₀ heterocyclicalkyl group, R₅′ is a substituted or unsubstituted C₁-C₂₀ alkyl group, a substituted or unsubstituted C₁-C₂₀ alkoxy group, a substituted or unsubstituted C₂-C₂₀ alkenyl group, a substituted or unsubstituted C₂-C₂₀ alkynyl group, a substituted or unsubstituted C₆-C₂₀ aryl group, a substituted or unsubstituted C₆-C₂₀ aryloxy group, a substituted or unsubstituted C₇-C₂₀ arylalkyl group, a substituted or unsubstituted C₂-C₂₀ heteroaryl group, a substituted or unsubstituted C₂-C₂₀ heteroaryloxy group, a substituted or unsubstituted C₂-C₂₀ heteroarylalkyl group, a substituted or unsubstituted C₄-C₂₀ carbocycle group, a substituted or unsubstituted C₄-C₂₀ carbocyclicalkyl group, a substituted or unsubstituted C₂-C₂₀ heterocycle group, or a substituted or unsubstituted C₂-C₂₀ heterocyclicalkyl group, R₆ is selected from the group consisting of a substituted or unsubstituted C₁-C₂₀ alkylene group, a substituted or unsubstituted C₂-C₂₀ alkenylene group, a substituted or unsubstituted C₂-C₂₀ alkynylene group, a substituted or unsubstituted C₆-C₂₀ arylene group, a substituted or unsubstituted C₂-C₂₀ heteroarylene group, —C(═O)—, and —SO₂—, wherein, at least one of R₅′ and R₆ is halogenated.
 2. The electrolyte membrane of claim 1, wherein the cross-linkable compound is at least one selected from the group consisting of polybenzimidazoles (PBI), a polybenzimidazole-base complex, polybenzthiazoles, polybenzoxazoles, and polyimides.
 3. The electrolyte membrane of claim 1, wherein an amount of the cross-linkable compound is in the range of 5 to 95 parts by weight based on 100 parts by weight of the total weight of at least one selected from the first benzoxazine-based monomer and the second benzoxazine-based monomer.
 4. The electrolyte membrane of claim 1, wherein R₅ in Formula 1 is one of the groups represented by formulae below:


5. The electrolyte membrane of claim 1, wherein R₁ through R₄ in Formula 1 are each independently hydrogen, F, a C₁-C₁₀ alkyl group, an allyl group, or a C₆-C₁₀ aryl group.
 6. The electrolyte membrane of claim 1, wherein R₆ in Formula 2 is —C(CF₃)₂—, —SO₂—, or —C(CH₃)₂—.
 7. The electrolyte membrane of claim 1, wherein R₅′ in Formula 2 is a phenyl group or one selected from groups represented by formulae below:


8. The electrolyte membrane of claim 1, wherein the first benzoxazine-based monomer of Formula 1 is a compound represented by Formula 3 or 4 below:


9. The electrolyte membrane of claim 1, wherein the second benzoxazine-based monomer of Formula 2 is a compound represented by Formula 5 below:


10. The electrolyte membrane of claim 1, further comprising a proton conductor.
 11. The electrolyte membrane of claim 10, wherein the proton conductor is a phosphoric acid or a C₁-C₂₀ organic phosphonic acid.
 12. A fuel cell comprising: a cathode; an anode; and the electrolyte membrane according to claim 1 disposed between the cathode and the anode.
 13. The fuel cell of claim 12, wherein at least one of the cathode and the anode has a catalyst layer comprising a catalyst and a polymer of at least one selected from the first benzoxazine-based monomer of Formula 1 and the second benzoxazine-based monomer of Formula 2,

wherein R₁ through R₄ are each independently hydrogen, a substituted or unsubstituted C₁-C₂₀ alkyl group, a substituted or unsubstituted C₁-C₂₀ alkoxy group, a substituted or unsubstituted C₂-C₂₀ alkenyl group, a substituted or unsubstituted C₂-C₂₀ alkynyl group, a substituted or unsubstituted C₆-C₂₀ aryl group, a substituted or unsubstituted C₆-C₂₀ aryloxy group, a substituted or unsubstituted C₂-C₂₀ heteroaryl group, a substituted or unsubstituted C₂-C₂₀ heteroaryloxy group, a substituted or unsubstituted C₄-C₂₀ cycloalkyl group, a substituted or unsubstituted C₄-C₂₀ cycloalkyloxy group, a substituted or unsubstituted C₂-C₂₀ heterocycle group, a halogen atom, a hydroxyl group, or a cyano group, R₅ is a halogenated C₁-C₂₀ alkyl group, a halogenated C₁-C₂₀ alkoxy group, a halogenated C₂-C₂₀ alkenyl group, a halogenated C₂-C₂₀ alkynyl group, a halogenated C₆-C₂₀ aryl group, a halogenated C₆-C₂₀ aryloxy group, a halogenated C₇-C₂₀ arylalkyl group, a halogenated C₂-C₂₀ heteroaryl group, a halogenated C₂-C₂₀ heteroaryloxy group, a halogenated C₂-C₂₀ heteroarylalkyl group, a halogenated C₄-C₂₀ carbocycle group, a halogenated C₄-C₂₀ carbocyclicalkyl group, a halogenated C₂-C₂₀ heterocycle group, or a halogenated C₂-C₂₀ heterocyclicalkyl group, R₅′ is a substituted or unsubstituted C₁-C₂₀ alkyl group, a substituted or unsubstituted C₁-C₂₀ alkoxy group, a substituted or unsubstituted C₂-C₂₀ alkenyl group, a substituted or unsubstituted C₂-C₂₀ alkynyl group, a substituted or unsubstituted C₆-C₂₀ aryl group, a substituted or unsubstituted C₆-C₂₀ aryloxy group, a substituted or unsubstituted C₇-C₂₀ arylalkyl group, a substituted or unsubstituted C₂-C₂₀ heteroaryl group, a substituted or unsubstituted C₂-C₂₀ heteroaryloxy group, a substituted or unsubstituted C₂-C₂₀ heteroarylalkyl group, a substituted or unsubstituted C₄-C₂₀ carbocycle group, a substituted or unsubstituted C₄-C₂₀ carbocyclicalkyl group, a substituted or unsubstituted C₂-C₂₀ heterocycle group, or a substituted or unsubstituted C₂-C₂₀ heterocyclicalkyl group, R₆ is selected from the group consisting of a substituted or unsubstituted C₁-C₂₀ alkylene group, a substituted or unsubstituted C₂-C₂₀ alkenylene group, a substituted or unsubstituted C₂-C₂₀ alkynylene group, a substituted or unsubstituted C₆-C₂₀ arylene group, a substituted or unsubstituted C₂-C₂₀ heteroarylene group, —C(═O)—, and —SO₂—, wherein, at least one of R₅′ and R₆ is halogenated.
 14. The fuel cell of claim 13, wherein the catalyst layer further comprises at least one binder selected from the group consisting of poly(vinyldenefluoride), polytetrafluoroethylene (PTFE), a tetrafluoroethylene-hexafluoroethylene copolymer, fluorinated ethylene propylene (FEP), styrene butadiene rubber (SBR), and polyurethane.
 15. The fuel cell of claim 14, wherein an amount of the binder is in the range of 0.1 to 50 parts by weight based on 100 parts by weight of the catalyst.
 16. The fuel cell of claim 14, wherein the catalyst layer further comprises a proton conductor.
 17. The fuel cell of claim 16, wherein the proton conductor is a phosphoric acid or a C₁-C₂₀ organic phosphonic acid.
 18. The fuel cell of claim 13, wherein R₅ in Formula 1 is one of the groups represented by formulae below:


19. The fuel cell of claim 13, wherein R₁ through R₄ in Formula 1 are each independently hydrogen, F, a C₁-C₁₀ alkyl group, an allyl group, or a C₆-C₁₀ aryl group.
 20. The electrolyte membrane of claim 13, wherein R₆ in Formula 2 is —C(CF₃)₂—, —SO₂—, or —C(CH₃)₂—.
 21. The electrolyte membrane of claim 13, wherein R₅′ in Formula 2 is a phenyl group or one selected from groups represented by formulae below:


22. The electrolyte membrane of claim 13, wherein the first benzoxazine-based monomer of Formula 1 is a compound represented by Formula 3 or 4 below.


23. The electrolyte membrane of claim 13, wherein the second benzoxazine-based monomer of Formula 2 is a compound represented by Formula 5 below.


24. The fuel cell of claim 13, wherein an amount of the polymer of at least one selected benzoxazine-based monomer is in the range of 0.1 to 50 parts by weight based on 100 parts by weight of the catalyst.
 25. An electrolyte membrane for a fuel cell, comprising: a crosslinked polybenzoxazine-based compound formed of a benzoxazine-based monomer represented by Formula 1 below crosslinked with a cross-linkable compound,

wherein R₁ through R₄ are each independently hydrogen, a substituted or unsubstituted C₁-C₂₀ alkyl group, a substituted or unsubstituted C₁-C₂₀ alkoxy group, a substituted or unsubstituted C₂-C₂₀ alkenyl group, a substituted or unsubstituted C₂-C₂₀ alkynyl group, a substituted or unsubstituted C₆-C₂₀ aryl group, a substituted or unsubstituted C₆-C₂₀ aryloxy group, a substituted or unsubstituted C₂-C₂₀ heteroaryl group, a substituted or unsubstituted C₂-C₂₀ heteroaryloxy group, a substituted or unsubstituted C₄-C₂₀ cycloalkyl group, a substituted or unsubstituted C₄-C₂₀ cycloalkyloxy group, a substituted or unsubstituted C₂-C₂₀ heterocycle group, a halogen atom, a hydroxyl group, or a cyano group, and R₅ is a halogenated C₁-C₂₀ alkyl group, a halogenated C₁-C₂₀ alkoxy group, a halogenated C₂-C₂₀ alkenyl group, a halogenated C₂-C₂₀ alkynyl group, a halogenated C₆-C₂₀ aryl group, a halogenated C₆-C₂₀ aryloxy group, a halogenated C₇-C₂₀ arylalkyl group, a halogenated C₂-C₂₀ heteroaryl group, a halogenated C₂-C₂₀ heteroaryloxy group, a halogenated C₂-C₂₀ heteroarylalkyl group, a halogenated C₄-C₂₀ carbocycle group, a halogenated C₄-C₂₀ carbocyclicalkyl group, a halogenated C₂-C₂₀ heterocycle group, or a halogenated C₂-C₂₀ heterocyclicalkyl group.
 26. An electrolyte membrane for a fuel cell, comprising: a crosslinked polybenzoxazine-based compound formed of a benzoxazine-based monomer represented by Formula 2 below crosslinked with a cross-linkable compound,

wherein R₅′ is a substituted or unsubstituted C₁-C₂₀ alkyl group, a substituted or unsubstituted C₁-C₂₀ alkoxy group, a substituted or unsubstituted C₂-C₂₀ alkenyl group, a substituted or unsubstituted C₂-C₂₀ alkynyl group, a substituted or unsubstituted C₆-C₂₀ aryl group, a substituted or unsubstituted C₆-C₂₀ aryloxy group, a substituted or unsubstituted C₇-C₂₀ arylalkyl group, a substituted or unsubstituted C₂-C₂₀ heteroaryl group, a substituted or unsubstituted C₂-C₂₀ heteroaryloxy group, a substituted or unsubstituted C₂-C₂₀ heteroarylalkyl group, a substituted or unsubstituted C₄-C₂₀ carbocycle group, a substituted or unsubstituted C₄-C₂₀ carbocyclicalkyl group, a substituted or unsubstituted C₂-C₂₀ heterocycle group, or a substituted or unsubstituted C₂-C₂₀ heterocyclicalkyl group, R₆ is selected from the group consisting a substituted or unsubstituted C₁-C₂₀ alkylene group, a substituted or unsubstituted C₂-C₂₀ alkenylene group, a substituted or unsubstituted C₂-C₂₀ alkynylene group, a substituted or unsubstituted C₆-C₂₀ arylene group, a substituted or unsubstituted C₂-C₂₀ heteroarylene group, —C(═O)—, and —SO₂—, wherein, at least one of R₅′ and R₆ is halogenated. 